An efficient process for preparing the trans isomeric form of 1,3,4,6,7,11b-hexahydro-7-aryl-2H-pyrazino[2,1-a]isoquinolines is disclosed. The process involves the use of novel compounds, 3-phenyl-4-arylacyl-2-piperazinones and 3-phenyl-4-(2-hydroxy-2-arylethyl)piperazines.